We should just pay for F16s (which are going to be retired by other NATO countries) to be sent to Ukraine.
It seems to me that we might be missing a trick here. I mean we have Challenger 2s which need upgrading to Challenger 3s by RheinMetal in Germany (because BAE bought the factories which made them here and closed them). We are in a situation where we are going to have an ever decreasing number of viable MBTs, as a smaller number are upgraded to C3 and then an even smaller number of those are eventually upgraded to C4, presumably in German factories.
Wouldn't it be better to do a deal with the yanks, whereby we send the Ukrainians all our Challenger 2 tanks, all their spare parts and all the ammunition we can scrape together for the foreseeable future for their non-NATO standard (rifled) main gun and in exchange the US gives us an equal number of the latest M1A2 Abrams MBTs? (If they won't go for that we could offer to pay them a zero interest balancing payment within, say, 10 years.)
That way we get a world-leading tank design which is fully compatible with other NATO forces. I mean for the last 40 years we have only fought with tanks alongside the USA/NATO anyway, so it's not like it isn't in their interests to make sure we have all the spare parts we need for them. I would trust the USA to keep us properly supplied much more than the Germans, especially in a World War 3 scenario where Germany would be on the front line!